The present invention relates to surgical methods and apparatus for applying an electrosurgical signal to a tissue site to achieve a predetermined surgical effect, and more particularly, to an improved electrosurgical instrument and method to achieve such effect with reduced attendant smoke generation at the surgical site.
The potential applications and recognized advantages of employing electrical energy in surgical procedures continue to increase. In particular, for example, electrosurgical techniques are now being widely employed to provide significant localized surgical advantages in both open and laparoscopic applications, relative to traditional surgical approaches.
Electrosurgical techniques typically entail the use of a hand-held instrument, or pencil, that transfers radio frequency (RF) electrical energy to a tissue site, a source of radio frequency (RF) electrical energy, and an electrical return path device, commonly in the form of a return electrode pad positioned under a patient (i.e. a monopolar system configuration) or a smaller return electrode positionable in bodily contact at or immediately adjacent to the surgical site (i.e. a bipolar system configuration). The waveforms produced by the RF source yield a predetermined electrosurgical effect, namely tissue cutting or coagulation.
Despite numerous advances in the field, currently-employed electrosurgical techniques often generate substantial smoke at the surgical site. Such smoke occurs as a result of tissue heating and the associated release of hot gases/vapor from the tissue site (e.g., in the form of an upward plume). As will be appreciated, any generation of smoke may impede observation of the surgical site during surgical procedures. Additionally, the generation of smoke results in attendant fouling of the atmosphere in the surgical theater. Clearly, these environmental impacts may adversely detract from the performance of medical personnel. Further, there is growing concern that the smoke may be a medium for the transport of pathogens away from the surgical site, including viruses such as HIV. Such concerns have contributed to the use of face shields and masks by surgical personnel.
To date, implemented approaches to deal with smoke have focused on the use of devices that either evacuate the smoke by sucking the same into a filtering system, or that merely blow the smoke away from the surgical site by a pressurized gas stream. Smoke evacuators typically require the movement of large amounts of air to be effective. As such, evacuators tend to be not only noisy but also space consuming. Approaches for blowing smoke away from the surgical site fail to address many of the above-noted concerns, since smoke is not actually removed from the surgical environment. Moreover, both of the above-noted approaches entail the use of added componentry, thereby increasing the cost and complexity of electrosurgical systems.
Accordingly, a primary objective of the present invention is to provide an apparatus and method for use in electrosurgery that results in reduced generation of smoke at a surgical site.
Another objective of the present invention is to provide an apparatus and method for use in electrosurgery that yields less eschar accumulation on the electrosurgical instrument utilized.
An additional objective of the present invention is to provide an apparatus and method for use in electrosurgery that provides for reduced charring along an electrosurgical incision.
Yet another objective is to realize one or more of the foregoing objectives in a manner which does not significantly impact space or cost requirements, and which maintains and potentially enhances the effectiveness of electrosurgical procedures.
In addressing these objectives, the present inventors have recognized that a large portion of the smoke generated utilizing known electrosurgical instruments results from the transmission of electrosurgical energy to tissue from areas of known electrosurgical instruments that are actually intended to be xe2x80x9cnon-functionalxe2x80x9d for purposes of achieving the desired electrosurgical effect (i.e. cutting or coagulation). That is, while known electrosurgical instruments include xe2x80x9cfunctionalxe2x80x9d portions which are designed to be selectively positioned to direct an electrosurgical signal to an intended surgical location (e.g. along a desired incision line), the discharge of energy is not effectively restricted to the functional portions.
More generally in this regard, energy discharge from electrosurgical instruments may be in the form of electrical energy and/or thermal energy. Electrical energy is transferred whenever the electrical resistance of a region between an electrosurgical instrument and tissue can be broken down by the voltage of the electrosurgical signal. Thermal energy is transferred when thermal energy that has accumulated in the electrosurgical instrument overcomes the thermal resistance between the instrument and the tissue (i.e. due to temperature differences therebetween).
The discharge of electrical and thermal energy from nonfunctional areas of known electrosurgical instruments results in unnecessary heating of tissue at a tissue site. In the case of electrical energy discharge, thermal energy is generated as a result of tissue resistance. As the amount of thermal energy at a tissue site increases, the electrical resistance at the surgical site also increases, thereby resulting in the further generation of heat. Such increased heating may in turn result in tissue charring as well as the splattering of tissue matter onto the electrosurgical instrument employed. The splattered tissue matter may accumulate as eschar on the electrosurgical instrument and present a further resistance/heat source to the surgical site. Eschar accumulation on electrosurgical instruments also raises the need for medical personnel to periodically suspend a procedure in order to clean the eschar from the electrosurgical instrument. As can be appreciated, such disturbances can adversely impact an electrosurgical procedure.
In short, the present inventors have recognized that any undesired and unnecessary discharge of electrosurgical energy from non-functional portions of an electrosurgical instrument to a surgical site can have a negative and cascading effect of unnecessary heat generation and resultant smoke generation, eschar build-up on the electrosurgical instrument and unnecessary tissue charring. In the later regard, it is believed that tissue charring may adversely affect healing.
In conjunction with the above-referenced recognition, the present invention provides an apparatus and method for reducing unnecessary/undesired electrical and/or thermal discharge during electrosurgical procedures. Such reduction(s) are achieved via enhanced localization of electrical and thermal energy transmission to a tissue site. More particularly, the present invention markedly reduces electrical/thermal discharge from non-functional areas of an electrosurgical instrument by insulating the nonfunctional areas and/or by providing for an effective level of heat removal away from functional portions of an electrosurgical instrument and/or by otherwise enhancing the localized delivery of an electrosurgical signal to a tissue site.
In this regard, the present invention comprises an electrosurgical instrument that includes a metal body for carrying an electrosurgical signal and an outer insulating layer positioned over at least a portion of the metal body (i.e., a non-functional portion). The metal body includes a main body portion and a peripheral edge portion, the peripheral edge portion being functional for the conveyance of the electrosurgical signal to a tissue site.
In one aspect of the present invention, the outer insulating layer may be advantageously provided to have a maximum thermal conductance of about 1.2 W/cm2-xc2x0 K when measured at about 300xc2x0 K, more preferably about 0.12 W/cm2-xc2x0 K or less when measured at about 300xc2x0 K, and most preferably about 0.03 W/cm2-xc2x0 K when measured at about 300xc2x0 K. For purposes hereof, thermal conductance is intended to be a measure of the overall thermal transfer across any given cross section (e.g. of the insulation layer), taking into account both the thermal conductivity of the materials comprising such layer and the thickness of the layer (i.e. thermal conductance of layer=thermal conductivity of material comprising the layer (W/cmxc2x0 K)/thickness of the layer (cm)). In relation to the foregoing aspect, the insulation layer should also exhibit a dielectric withstand voltage of at least the peak-to-peak voltages that may be experienced by the electrosurgical instrument during surgical procedures. The peak voltages will depend upon the settings of the RF source employed, as may be selected by clinicians for particular surgical procedures. For purposes of the present invention, the insulation layer should exhibit a dielectric withstand voltage of at least about 50 volts, and more preferably, at least about 150 volts. As employed herein, the term dielectric withstand voltage means the capability to avoid an electrical breakdown (e.g. an electrical discharge through the insulating layer).
In one embodiment, the outer insulating layer advantageously comprises a polymeric compound. More particularly, such polymeric compound includes at least about 10% (by weight), and most preferably at least about 20% (by weight), of a component selected from a group comprising: silicon and carbon. In this regard, silicon-based, polymeric insulating layers have been found to be of particular benefit. Such silicon-based, polymeric layers have a thermal conductivity of about 0.003 W/cmxc2x0 K or less when measured at about 300xc2x0 K. Such silicon-based, polymeric layers have been found to be effective when having a thickness of about 0.25 mm or more. Further, such silicon-based, polymeric layers have a dielectric strength of at least about 12 Kv/mm. In a related embodiment, the insulation layer may comprise polytetrafluoroethylene.
In another embodiment, the insulating layer may comprise a ceramic material (e.g., applied to the metal body via dipping, spraying, etc, then cured via drying, firing, etc.). Preferably, the ceramic insulating layer should be able to withstand temperatures of at least about 2000xc2x0 F. The ceramic insulating layer may comprise various metal/non-metal combinations, including for example compositions that comprise the following: aluminum oxides (e.g. alumina and Al2O3), zirconium oxides (e.g. Zr2O3), zirconium nitrides (e.g. ZrN), zirconium carbides (e.g. ZrC), boron carbides (e.g. B4C), silicon oxides (e.g. SiO2), mica, magnesium-zirconium oxides (e.g. (Mgxe2x80x94Zr)O3), zirconium-silicon oxides (e.g. (Zrxe2x80x94Si)O2), titanium oxides (e.g., TiO2) tantalum oxides (e.g. Ta2O5), tantalum nitrides (e.g. TaN), tantalum carbides (e.g., TaC), silicon nitrides (e.g. Si3N4), silicon carbides (e.g. SiC), tungsten carbides (e.g. WC) titanium nitrides (e.g. TiN), titanium carbides (e.g., TiC), nibobium nitrides (e.g. NbN), niobium carbides (e.g. NbC), vanadium nitrides (e.g. VN), vanadium carbides (e.g. VC), and hydroxyapatite (e.g. substances containing compounds such as 3Ca3(PO4)2Ca(OH)2 Ca10(PO4)6(OH)2 Ca5(OH)(PO4)3, and Ca10H2O26P6). One or more ceramic layers may be employed, wherein one or more layers may be porous, such as holes filled with one or more gases or vapors. Such porous compositions will usually have lower thermal conductivity than the nonporous materials. An example of such materials are foam e.g., an open cell silicon carbide foam.
As may be appreciated, in other embodiments the insulating layer may be defined by at least one inner layer (e.g. adjacent to the metal body) that includes a ceramic material, and at least one outer layer that comprises a polymeric compound as noted above. Such inner and outer layers may be advantageously employed to yield an average maximum thermal conductivity of about 0.006 W/cm-xc2x0 K or less where measured at 300xc2x0 K. The inner layer and outer layer may preferably each have a thickness of between about 0.001 and 0.2 inches, and most preferably between about 0.005 and 0.100 inches.
In another aspect of the present invention, the metal body of the inventive electrosurgical instrument may be provided to have a thermal conductivity of at least about 0.35 W/cmxc2x0 K when measured at about 300xc2x0 K. By way of primary example, the metal body may advantageously comprise at least one metal selected from a group comprising: silver, copper, aluminum, gold, tungsten, tantalum, columbium (i.e., niobium), and molybdenum. Alloys comprising at least about 50% (by weight) of such metals may be employed, and even more preferably at least about 90% (by weight). Additional metals that may be employed in such alloys include zinc.
In yet another aspect of the present invention, at least a portion of the peripheral edge portion of the metal body is not insulated (i.e. not covered by the outer insulating layer). In connection therewith, when the outer peripheral edge portion comprises copper such portion may be coated (e.g. about 10 microns or less) with a biocompatible metal. By way of example, such biocompatible metal may be selected from the group comprising: nickel, silver, gold, chrome, titanium tungsten, tantalum, columbium (i.e., niobium), and molybdenum.
In an additional aspect of the invention, it has also been determined that a laterally tapered, or sharpened, uninsulated peripheral edge portion having a maximum cross-sectional thickness which is about {fraction (1/10)} of the maximum cross-sectional thickness of the main body portion is particularly effective for achieving localized electrosurgical signal delivery to a tissue site. In the later regard, it has also been determined preferable that the outer extreme of the peripheral edge portion of the metal body have a thickness of about 0.001 inches or less.
In an additional related aspect of the present invention, the metal body may comprise two or more layers of different materials. More particularly, at least a first metal layer may be provided to define an exposed peripheral edge portion of the metal body that is functional to convey an electrosurgical signal to tissue as described above. Preferably, such first metal layer may comprise a metal having a melting temperature greater than about 2600xc2x0 F., more preferably greater than about 3000xc2x0 F., and even more preferably greater than about 4000xc2x0 F., thereby enhancing the maintenance of a desired peripheral edge thickness during use (e.g. the outer extreme edge noted above). Further, the first metal layer may preferably have a thermal conductivity of at least about 0.35 W/cmxc2x0 K when measured at 300xc2x0 K.
For living human/animal applications, the first metal layer may comprise a first material selected from a group consisting of tungsten, tantalum, columbium (i.e., niobium), and molybdenum. All of these metals have thermal conductivities within the range of about 0.5 to 1.65 W/cmxc2x0 K when measured at 300xc2x0 K. Preferably, alloys comprising at least about 50% by weight of at least one of the noted first materials may be employed, and even more preferably at least about 90% by weight.
In addition to the first metal layer the metal body may further comprise at least one second metal layer on the top and/or bottom of the first metal layer. Preferably, a first metal layer as noted above is provided in a laminate arrangement between top and bottom second metal layers. To provide for rapid heat removal, the second metal layer(s) preferably has a thermal conductivity of at least about 2 W/cmxc2x0 K. By way of primary example, the second layer(s) may advantageously comprise a second material selected from a group consisting of copper, gold, silver and aluminum. Preferably, alloys comprising at least about 50% of such materials may be employed, and even more preferably at least about 90% by weight. It is also preferable that the thickness of the first metal layer and of each second metal layer (e.g. for each of a top and bottom layer) be defined at between about 0.001 and 0.25 inches, and even more preferably between about 0.005 and 0.1 inches.
As may be appreciated, multi-layered metal bodies of the type described above may be formed using a variety of methods. By way of example, sheets of the first and second materials may be role-bonded together then cut to size. Further, processes that employ heat or combinations of heat and pressure may also be utilized to yield a laminated metal body.
In a further aspect of the present invention, the inventive electrosurgical instrument may further comprise a heat sink for removing thermal energy from the metal body. In this regard, the provision of a heat sink establishes a thermal gradient away from the peripheral edge of the metal body, thereby reducing undesired thermal transfer to a tissue site. More particularly, it is preferable for the heat sink to operate so as to maintain the maximum temperature on the outside surface of the insulating layer at about 160xc2x0 C. or less, more preferably at about 80xc2x0 C. or less, and most preferably at 60xc2x0 C. or less. Relatedly, it is preferable for the heat sink to operate to maintain an average metal body temperature of about 500xc2x0 C. or less, more preferably of about 200xc2x0 C. or less, and most preferable of about 100xc2x0 C. or less.
In one approach, the heat sink may comprise a vessel comprising a phase change material that either directly contacts a portion of the metal body (e.g. a support shaft portion) or that contacts a metal interface provided on the vessel which is in turn in direct contact with a portion of the metal body (e.g. a support shaft portion). Such phase change material changes from a first phase to a second phase upon absorption of thermal energy from the metal body. In this regard, the phase change temperature for the material selected should preferably be greater than the room temperature at the operating environment and sufficiently great as to not change other than as a consequence of thermal heating of the electrosurgical instrument during use. Such phase change temperature should preferably be greater than about 30xc2x0 C. and most preferably at least about 40xc2x0 C. Further, the phase change temperature should be less than about 225xc2x0 C. Most preferably, the phase change temperature should be less than about 85xc2x0 C.
The phase change may be either from solid to liquid (i.e., the phase change is melting) or from liquid to vapor (i.e., the phase change is vaporization) or from solid to vapor (i.e., the phase change is sublimation). The most practical phase changes to employ are melting and vaporization. By way of example, such phase change material may comprise a material that is an organic substance (e.g., fatty acids such as stearic acid, hydrocarbons such as paraffins) or an inorganic substance (e.g., water and water compounds containing sodium, such as, sodium silicate (2-)-5-water, sodium sulfate-10-water).
In another approach, the heat sink may comprise a gas flow stream that passes in direct contact with at least a portion of the metal body. Such portion may be a peripheral edge portion and/or a shaft portion of the metal body that is designed for supportive interface with a holder for hand-held use. Alternatively, such portion may be interior to at least a portion of the metal body, such as interior to the exposed peripheral edge portion and/or the shaft portion of the metal body that is designed for supportive interface with a holder for hand-held use. In yet other approaches, the heat sink may simply comprise a thermal mass (e.g. disposed in a holder).
In one arrangement of the present invention, an electrosurgical instrument comprises a main body portion having a blade-like configuration at a first end and an integral, cylindrical shaft at a second end. The main body may comprise a highly-conductive metal and/or multiple metal layers as noted. At least a portion of the flattened blade end of the main body is coated with a ceramic-based and/or silicon-based, polymer insulating layer, except for the peripheral edge portion thereof. The cylindrical shaft of the main body is designed to fit within an outer holder that is adapted for hand-held use by medical personnel. Such holder may also include a chamber comprising a phase-change material or other heat sink as noted hereinabove. Additionally, electrical, push-button controls may be incorporated into the holder for selectively controlling the application of one or more, predetermined, electrosurgical signal(s) from an RF energy source to the flattened blade via the shaft of the main body portion.
In the latter regard, conventional electrosurgical signals may be advantageously employed in combination with one or more of the above-noted electrosurgical instrument features. In particular, the inventive electrosurgical instrument yields particular benefits when employed with electrosurgical signals and associated apparatus of the type described in U.S. Pat. No. 6,074,387, hereby incorporated by reference in its entirety.
Numerous modifications and additions to the present invention will be apparent to those skilled in the art upon consideration of the further description that follows.